Copper Capillary Tube Research Articles

Fundamental Study on Heat Transport Device for Effective Utilization of Unused Heat

Recently, many countries have become increasingly interested in unused but possibly useful energy resources. Among these unused resources, the thermal energy produced around us can be used as a potential energy source for heating, cooling and power generation. This thermal energy is relatively stable on the supply side as waste heat in the industrial field. Heat transport devices are one of the important technology for the effective use of unused heat energy. This paper conducts basic research on devices that effectively transport heat below 200ºC. A pulsating heat pipe (PHP) is an excellent heat transport device based on the phase change of a working fluid. Experiments are performed to investigate the thermal performance of a PHP using different working fluids. The PHP consists of 20 parallel channels made of a copper capillary tube with an internal diameter of 1.8 mm. The PHP is filled with deionized water and an aqueous solution of 1-butanol as working fluids, with different filling ratios (FRs) in the range 50-60 vol.%. The 1-butanol aqueous solution is known as a self-rewetting fluid. The experimental results indicate that, in the case of self-rewetting fluid, stable oscillating motion in the PHP arises at the heat load regime lower than that with water. In addition, the effective thermal conductivity of the PHP with the highest concentration of self-rewetting fluid is higher than that with other fluids in the high heat load regime.

Flow-induced noise generation at the outlet of a capillary tube

The aim of this work is the identification of noise generation mechanisms at the outlet of an adiabatic capillary tube used as throttling device in a cooling cycle. For this purpose, experiments are carried out on a R-600a test bench designed for systematic investigations on flow-induced capillary noise. The experiments are performed using a copper capillary tube with an inner diameter of 0.6 mm. The test bench enables process control with a continuous change of the capillary outlet pressure, while the inlet pressure and temperature remain constant. A similar process takes place in a refrigerator at the beginning of the on-cycle, when the compressor starts to pull down the evaporation pressure. Correlations between various operating conditions and the emitted airborne noise can thus be established. The evaluation of the sound pressure level profiles provides a method to indicate the change of flow regimes at the capillary tube outlet, using flow pattern maps from literature. We identify two different noise generation mechanisms: In case of intermittent flow regimes, pressure pulses evoked by the fluid lead to fluctuating unsteady noise excitations. During non-intermittent flow regimes, on the other hand, uniform noise excitations strongly correlate with the vapor velocity of the two-phase flow.

Spatial Temperature Distribution of an Open Square Capillary Tube Wall during Passage of a Taylor Liquid Plug

Taylor plug/bubble flow is a predominant two-phase flow pattern occurring in several microfluidic devices such as in microchannel heat sinks, fuel cells, pulsating heat pipes, labon-chips, microreactors, etc. Such flows are characterized by an alternating sequence of liquid plug and gas bubbles, whose ensuing local transport characteristics (heat and mass transfer) are complex and still not fully understood. Presence of gas-liquid interfaces, thin-film dynamics, moving contact lines, wettability, contact angle hysteresis, are some of the physical phenomena involved in Taylor bubble flow systems that manifests into its complex transport characteristics. Understanding the local interfacial transport mechanism is of vital importance to develop a comprehensive model for micro-scale devices utilizing Taylor bubble flow. In this background, we probe locally into the local thermo-hydrodynamics of ‘unit-cell’ of Taylor plug flow, which is essentially an isolated liquid plug moving inside a mini square capillary copper tube (side = 2 mm), surrounded by gas from both its sides, and try discerning local evaporation dynamics, with the help of IR thermography. This study focuses on the interplay of conjugate conduction, local thin film hydrodynamics formed behind the moving liquid plug, and its subsequent evaporation. We obtain local temperature distribution in the meniscus region, as the plug moves through the capillary tube. As the cold plug passes through the tube, local temperatures drop drastically, the transient reaches the heater-tube interface a bit delayed and there the drop in temperature is modest. The study clearly reveals that there is a strong thermo-hydrodynamic coupling between the tube wall and the moving Taylor liquid plug.

Research on Heat Transfer Performance of the Open-Loop Micro Pulsating Heat Pipe with Self-Rewetting Fluids

As technology becomes increasingly miniaturized, extremely localized heat dissipation leads to the challenge of how to keep these devices from overheating. A pulsating heat pipe (PHP) is an excellent cooling device based on the phase change of a working fluid. Experiments are performed to investigate the thermal performances of a Micro Pulsating Heat Pipe (MPHP) using different working fluids. The MPHP consists of 20 parallel channels made of a copper capillary tube with an internal diameter of 0.8 mm. The MPHP is filled with ethanol, deionized water and an aqueous solution of 1-butanol as working fluids, with different filling ratios (FRs) in the range 40–70 vol.%. The 1-butanol aqueous solution is known as a self-rewetting fluid, i.e. a dilute aqueous solution of alcohols with a number of carbon atoms higher than four (such as 1-butanol and pentanol). The surface tension of self-rewetting fluids decreases gradually with an increase in temperature, reaching a minimum around 60 °C, and subsequently increases gradually at higher temperatures. Therefore, at relatively high temperature self-rewetting fluids flow towards the regions at higher temperature due to the Marangoni effect. This flow should improve the boiling phenomenon, which is very important in the heat transfer mechanism of the MPHP. The experimental results indicate that, in the case of self-rewetting fluid, the stable oscillating motion in the MPHP arises at the heat load regime lower than that with water. In addition, the effective thermal conductivity of the MPHP with the highest concentration of self-rewetting fluid is higher than that with other fluids in the high heat load regime.

Effect of position of heat mode to heat transfer of a closed loop oscillating heat pipe with check valves on fins

This research aimed to determine the effect of position of heat mode to closed loop oscillating heat pipe with check valves (CLOHP/CV) on fins. To check on heat transfer rate needed to focus on evaporator temperature, air velocity, and position of heat mode. All heat exchangers used ethanol as working fluid with the filling ratio of 50% by total volume of tube, evaporator temperature at 60, 70, and 80 degrees Celsius, and air velocity at 0.5, 1.0, and 1.5 meter per second, size of fin was 0.5 centimetre. All heat exchangers used different positions at evaporator section and condenser section of heat pipe. The CLOHP/CV was made from copper capillary tube of (inner diameter: 5 mm), 24 turns 2 check valves. The length of evaporator and condenser and adiabatic section is 20, 20, and 10 centimetre respectively. From the experiment it’s was found that the heat exchanger of bottom heat mode had a temperature of 80 degrees Celsius and air velocity of 1.5 m/s with heat flux and thermal effectiveness the highest.

Heat transfer characteristics of a novel closed-loop pulsating heat pipe with a check valve

A spring-loaded check valve controlling the one-way circulatory flow of the working fluid was integrated into an initial closed-loop pulsating heat pipe (CLPHP) to improve the thermal performance. The thermal performance of the CLPHP with a spring-loaded check valve (CLPHP/CV) was experimentally investigated and compared to the initial CLPHP. The initial CLPHP was made of a copper capillary tube with an inner diameter of 3 mm and ten spiral loops. The spring-loaded check valve was integrated into two locations in the initial CLPHP: between the two heating (CLPHP/CVh) sections and the two cooling (CLPHP/CVc) sections. Tests were conducted under three orientations: bottom, horizontal, and top heating modes. The CLPHP was charged with deionized water as the working fluid with a filling ratio of 60% by volume. The experimental results show that the check valve creates a one-way circulatory flow of the working fluid and facilitates the start-up of the CLPHP. A 25% decrease in thermal resistance of the CLPHP/CV is achieved compared with the initial CLPHP under top heating mode at a low heating load. Moreover, the check valve decreases the sensitivity of the CLPHP to its orientation, particularly when the check valve is integrated between the two heating sections.

Investigation and predictation of optimum meandering turn number of vertical and horizontal closed-loop pulsating heat pipes

The objectives of this study are to experimentally investigate the effect of meandering turn numbers on thermal performance and to predict the optimum meandering turn number of vertical and horizontal closed-loop pulsating heat pipes (CLPHP). The CLPHPs were made from a copper capillary tube with internal diameter of 2.0 mm. The CLPHPs were bent into undulating tubes with various meandering turn numbers, such as 5, 7, 10, 16, and 30. Each set of the CLPHPs had different evaporator section lengths of 50 mm and 150 mm. Heat input was supplied to the CLPHP by allowing the flow of distilled water as the heating medium through the evaporator section. The adiabatic section temperature was constantly controlled at 50°C. It could be concluded that the optimum meandering turn number of vertical CLPHPs with an evaporator section length of 50 mm is 10 for both R123 and water, and the optimum meandering turn numbers of vertical CLPHPs with an evaporator section length of 150 mm are 5 and 10, respectively, for R123 and water. However, the optimum meandering turn number of the horizontal CLPHP could not be found since the heat flux directly varies with the turn number. In addition, the correlation to predict the optimum meandering turn number of the vertical CLPHP was successfully established.

Thermal performance of Pulsating Heat Pipe on Electric Motor as Cooling Application

Heat generated in an electric motor can increase the operating temperature. The excessive operating temperature will reduce the electric motor performance and shorten the service life. An appropriate thermal management system is required to reduce the electric motor operating temperature. The objective of this study is to determine the thermal performance of pulsating heat pipes which applied to the electric motor thermal management system. A prototype of electric motor thermal management system was made from an induction motor with a cartridge heater instead of a heat-generating rotor and stator. Six pieces of pulsating heat pipe were mounted using hexagonal heat pipe holder which placed inside the electric motor housing. The pulsating heat pipes are made of a copper capillary tube using acetone as working fluid with a filling ratio of 0.5. The electric power input was varied from 30 W to 150 W. The use of pulsating heat pipes can reduce the electric motor surface temperature by 55.3°C with the minimum thermal resistance of 0.151°C/W.

Effects of filling ratio and condenser temperature on the thermal performance of a neon cryogenic oscillating heat pipe

A cryogenic oscillating heat pipe (OHP) made of a bended copper capillary tube is manufactured. The lengths of the condenser section, adiabatic section and evaporator section are 100, 280 and 100 mm, respectively. Neon is used as the working fluid. Effects of liquid filling ratio and condenser temperature on the thermal performance of the OHP are studied. A correlation based on the available experimental data sets is proposed to predict the thermal performance of the neon cryogenic OHP with different filling ratios and condenser temperature. Compared with the experimental data, the average standard deviation of the correlation is about 15.0%, and approximately 92.4% of deviations are within ±30%.

Thermal Performance of Oscillating Heat Pipe with Ethanol/Methanol for Heat Recovery Application Design

As one of the two-phase heat transfer technology, Oscillating Heat Pipe (OHP) gains popularity in heat pipe technology recently. OHP has an excellent performance, simple structure, low production cost and high flexibility for a wide range of applications. OHP is also suitable for applications in waste heat recovery system. This paper experimentally examines a closed loop OHP design for heat recovery application. Therefore, an OHP was manufactured and tested to find out the thermal characteristics for heat recovery application. OHP was made from capillary copper tube with 1.6 mm inner diameter based on the critical diameter for ethanol and methanol working fluids. The length of OHP evaporator, adiabatic and condenser were 260, 240 and 260 mm respectively. The total length of the OHP was 13.6 m and had 18 U-turns. The result showed that evaporator temperature for methanol was lower than ethanol at high heating input. Quasi-sine wave oscillation occurs at methanol OHP (Q=64 Watt). Methanol also had the lowest thermal resistance which was 0.258 °C/W at 79.5 Watt heat input.

A study on thermal performance of parallel connected pulsating heat pipe

A series of experiments were performed to investigate thermal performance of single, parallel connected and two turns pulsating heat pipe (PHP) using different working fluids. The copper capillary tube was used which has internal and external diameter 2.2mm and 3.2mm respectively. The PHP was filled with ethanol and deionized (DI) as working fluids with filling ratio 50%. Theoretical thermal resistance of parallel connected PHP was obtained using the experimental results of single turn PHP. DI water needs more input power to vaporize and startup than ethanol because boiling temperature and specific heat of DI water are larger than that of ethanol. At low input power, temperature of the PHP filled with DI water was not oscillated which means the device operates as thermosyphon. But temperature of the PHP filled with ethanol fluctuated at low input power which means liquid slug and vapor plug moves inside of the device. Thus, thermal resistance of the PHP filled with ethanol is lower than DI water which means ethanol is preferred as working fluid. Parallel connected pulsating heat pipe shows better thermal performance than two turns one from 42W to 50W for both working fluids because the effect of pressure drop is larger than the effect of increased perturbation.

Self-Pressurised Rapid Freezing (SPRF): an easy-to-use and low-cost alternative cryo-fixation method for nematodes

Self-Pressurised Rapid Freezing (SPRF), an easy-to-use and low-cost alternative cryo-fixation method, was evaluated based on a comparative analysis of the ultrastructure of spermatozoa of the nematodesAcrobeles complexusandCaenorhabditis elegans. Sealed copper tubes, packed with active nematodes in water, were plunged into nitrogen slush, a semi-solid form of nitrogen. The water inside the capillary copper tube expands upon cooling due to the formation of hexagonal ice, thereby generating high pressure intrinsically for cryo-fixation of the sample. For sperm cells cryo-fixed by SPRF, the preservation of the ultrastructure was comparable to that achieved with high pressure freezing. This was evidenced by the clear details in mitochondria, membranous organelles and cytoskeleton in the pseudopod. It was demonstrated that SPRF fixation did not destroy antigenicity, based on the results of the immunolocalisation of the major sperm protein in both species. In conclusion, SPRF is a low-cost alternative cryo-fixation method for nematodes.

Experimental Investigation on Thermal Performance of a Closed Loop Pulsating Heat Pipe without Fin and with Fin Structure

Pulsating Heat Pipe (PHP) is a new and emerging cooling technique in the field of thermal management especially in microelectronics. To fulfill the increasing demand of power electronic applications, PHP is a proven technology which works on principle of self-oscillation of the working fluid and phase change heat transfer phenomenon in a capillary tube. In this paper, the thermal performance of a closed loop pulsating heat pipe (CLPHP) without fin and with fin at the condenser section by using Acetone and Water as working fluid has been investigated experimentally. The effects of different parameters include the filling ratios (from 40% to 70% in steps of 10%), the inclination angles ( 0°, 30°, 45°, and 60°), and at various heat input (10 to 10W in the steps of 10W) has been investigated thoroughly. In this study CLPHP is made from long capillary copper tube with inner diameter of 2.0 mm and outer diameter of 3.0 mm. The heat pipe is bent into eighth number of U-turns and divided into three sections, evaporator section (50 mm), adiabatic section (120 mm) and condenser section (80 mm). Adiabatic section is maintained by using aluminum foil surrounded by appropriate insulation. The result shows that, the thermal resistance decreases as heat input increases. But at low heat input i.e. up to 60W, the thermal resistance decreases rapidly and the PHP performance is more sensitive to the inclination angle whereas high heat input i.e. above 60W, the thermal resistance decreases slowly and comparatively less independent to the inclination angle. Evaporator dry out is occurred for acetone at low filling ratio with 40% and 50% at heat input 40W and 50 W respectively. CLPHP with fin structure shows better performance than the CHPHP without fin structure at high heat input. Acetone with 70% filling ratio and water with 50% filling ratio shows the best performance at 0° inclination angle for both structures.

Development of a pulsating heat pipe with a directional circulation of a working fluid

The paper presents the results of development and experimental investigation of a pulsating heat pipe (PHP) with check valves (CV). The PHP was made of a copper capillary tube with an inside diameter of 1.25mm and curved in the form of a flat spiral with a total of 40 turns. The PHP was joined to an aluminum plate, which served as a thermal interface for contact with the heat-load source and sink. The working fluid was freon R-152a. Tests were conducted to compare the efficiency of two types of CV: one was patterned after a capillary barrier, the other, after a floating ball valve. The tests were carried out in the horizontal mode and the top heat mode. The results of the experiments have shown the high efficiency of ball check valves and the inefficiency of capillary barriers for organizing a directional circulation of a working fluid. It was shown that ball check valves made it possible to organize a directional circulation of a working fluid. At the cost of this the isothermality of the PHP heating zone increases, and its thermal resistance and orientation sensitivity decrease. Besides, the value of the limiting heat load increases by 10–14%.

Study on the performance of double-pipe air gap membrane distillation module

Air gap width has an important influence on the performance of air gap membrane distillation (AGMD) process. In this study, a novel double-pipe AGMD module (DP-AGMD-M) consisted of PVDF hollow fiber membrane and heat exchange capillary copper tubes was successfully developed. The evenly distribute and easily control of the air gap width in DP-AGMD-M can be implemented. The effect of the air gap width (da), hot feed temperature (T1), hot feed flow rate (Q), temperature difference (ΔT) between the hot feed outlet temperature and the cold feed inlet temperature, and the effective membrane module length (L) on the performance of DP-AGMD-M were experimental studied. The concept of the equivalent membrane distillation flux (JAGMD) was firstly introduced in this paper and used to evaluate the comprehensive performance of DP-AGMD-M. The optimal performances, including membrane distillation flux (J), gained output ratio (GOR) and JAGMD were obtained. Within the experimental range, the maximum J arrived at 11.4kg/(m2·h), the maximum GOR reached 6.6 and the maximum JAGMD was 29.6kg/(m2·h).

CFD and Volume Fraction Analysis of Closed Loop Pulsating Heat Pipe(CLPHP)

The Closed loop pulsating heat pipes (CLPHPs) are complex heat transfer devices having a strong thermo hydrodynamic coupling governing the thermal performance. Attempts are made to design, fabricate and test a closed loop pulsating heat pipe. In this experiment three different configurations of copper capillary tubes having internal diameters the total length and diameter of the channel is 540 mm and 1.95 mm respectively; and the pipe is made of copper. In this work, acetone-acetone vapor is taken as the working fluid for analysis. The experiments are conducted on vertical orientations for different heat loads as working fluids for fill ratio viz. 60%, the temperature distribution across the heat pipe was measured and recorded using thermocouples. The performance parameters such as temperature difference between evaporator and condenser, thermal resistance and the overall heat transfer coefficient are evaluated. The experimental results demonstrate the heat transfer characteristics, lower thermal resistance and higher heat transfer coefficient of PHP are found to be better at a fill ratio of 60% for various heat input and also the thermal performance of set up of pulsating heat pipe gives better result over the uniform diameter CLPHP the CFD analysis is done with the help of Ansys15.0 software.

Evolution of defects in the production of capillary copper tubes

Features of capillary copper tubes include small internal diameter, increased wall thickness and a specified throughput capacity. This research aimed to reveal the reasons of throughput capacity fluctuations. Manufacturing processes include piercing, hot extrusion and drawing. Defects such as inclusions and pores can occur during all the stages of manufacturing. Inclusions were studied employing scanning electron microscopy. The emergence of porous structures surrounding the inclusions was revealed. It was shown that during drawing such pores turn into channels, which can be later destroyed due to pressure. This process was calculated and analyzed using the ABAQUS finite element analysis software. It was further demonstrated that the inner surface of capillary copper tubes could be destructed along with accumulation of sludge, which would be the cause of throughput capacity fluctuations.

Operational Characteristics of the Oscillating Heat Pipe with Noncondensable Gas

In this study, the effects of noncondensable gas on the behavior of oscillating heat pipes were investigated. The oscillating heat pipe was made of capillary copper tube, and its turn number was 16. The working fluid used was ethanol, and argon gas was used as noncondensable gas. Experiments were conducted using four different noncondensable gas volume ratios. The temperature and inner pressure of the oscillating heat pipe were measured over a heat input range from 40 to 180 W. The results of this study suggest that the operating characteristics of the oscillating heat pipe were affected by noncondensable gas. In particular, the thermal resistance of the oscillating heat pipe increased with lower heat input as the amount of noncondensable gas increased. In addition, the thermal performance rapidly deteriorated with a large amount of noncondensable gas after local dryout. With higher heat input, the thermal resistance increased even with small noncondensable gas amounts.

Evaporation of a liquid film deposited on a capillary heated tube: Experimental analysis by infrared thermography of its thermal footprint

Evaporation of thin film deposited downstream menisci of slug flows is of major importance in the two-phase heat transfer phenomena occurring inside micro/mini-channels or in pulsating heat pipes. The aim of this study is consequently to analyze, by means of experimental infrared thermography, the heat transfers involved in the motion of a semi-infinite slug flow (one liquid slug followed by one single vapour bubble) in a heated capillary copper tube. Between the liquid and vapour phases the meniscus deposits a thin liquid film at the wall; this film brings about intense heat transfer at the wall by evaporation, leading to a highly significant decrease of external wall temperature. This phenomenon is better understood using infrared temperature measurements, which help to analyze the heat transfer characteristics present during evaporation. Given the highly transient nature of the process, the thickness of the deposited film is a parameter of major importance. After validation of the measurement method with tests involving no fluid or only liquid flow, the experimental results, with water being used as a working fluid, are compared to those of a numerical thermal model of which the parameters are well-known. The results drawn from the model rather accurately predict those obtained in the experiments and facilitate further analysis by presenting, for example, the evolution of liquid film thickness or heat flux density in conjunction with the wall temperature fields. It has been found that the thin film length is a first-order function of the initial thickness of the deposited film, the meniscus velocity, and the heat flux density at the wall, including the release of stored heat energy in the wall that is caused by the temperature difference before and after passage of the meniscus. This study represents a step towards better understanding the local physical phenomena governing the operation of pulsating heat pipes.

Experimental investigations on operating characteristics of a closed loop pulsating heat pipe

The operating mechanism of the pulsating heat pipe (PHP) is not well understood and the present technology cannot predict required design parameters for a given task. The aim of research work presented in this paper is to better understand the operation regimes of the PHP through experimental investigations. A series of experiments were conducted on a closed loop PHP with 5 turns made of copper capillary tube of 2 mm in inner diameter. Two different working fluids viz. ethanol and acetone were employed. The operating characteristics were studied for the variation of heat input, filling ratio (FR) and inclination angle of the tested device. The results strongly demonstrate the effect of the filling ratio of the working fluid on the operational stability and heat transfer capability of the device. Important insight into the operational characteristics of PHP has been obtained.